Currently, since the grid snap and rotation settings are hidden away in the Tool Settings menu, it’s easy to forget whether they’re on or off when you’re not using it. This is particularly bad if you’re copying properties from objects on the ceiling to those on the floor, or from those on opposite walls, as accidentally enabling the set rotation option can cause the object to flip upside-down into the ground/wall.
An easy solution would be to make the options visible outside of the menu, like so: